Environmental Control of Cloud-to-Ground Lightning Polarity in Severe Storms

Abstract

In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and CG flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong updrafts and associated large liquid water contents in severe storms lead to enhanced positive charging of graupel and hail via the noninductive charging mechanism, the generation of an inverted charge structure, and increased positive CG lightning production. The corollary is that environmental conditions favoring these

Lightning activity in Brazilian thunderstorms during TROCCINOX: implications for NO<sub>x</sub> production

“…Contrarily, Rutledge and MacGorman (1988) first suggested that the origin of charge for positive ground flashes in the trailing-stratiform region of MCSs was the rearward advection of positive charge on large aggregates of ice particles from the MCS convective charge centre (leading line) by the mesoscale storm-relative winds (now known as "charge advection mechanism"). More recently, these mechanisms have also been discussed by Gilmore and Wicker (2002), Carey et al (2005), Carey and Buffalo (2007) and Steiger et al (2007a, b). However, the VHF lightning observations by Carey et al (2005) clearly indicate that the "tilted dipole mechanism" and the "charge advection mechanism" are two different mechanism on different scales (convective and mesoscale) that should be considered separately.…”

Electrical Role for Severe Storm Tornadogenesis (and Modification)

“…More recently, a primary role for electrical force was brought in as a facilitator of IC tornadogenesis by Patton, Bothun and Sessions [54] with focus on the fact that many tornadic vortices begin at storm mid-level and build downward into ground level tornadoes, more or less in the same manner as originally described by Vonnegut [2,3]. Important connection was established with conditions of high wind shear and large CAPE, in the latter case as already mentioned for the description given in the detailed analysis reported by Carey and Buffalo [20]. In the Patton et al model, a midlevel embryonic tornado structure, enhanced by electrical action, is taken to lead to a central downdraft that acts to build the vortex rotation in a downward direction.…”

“…The doubly-shaded geographical region covered in Figure 1 may be compared with the not-too-different similarly outlined area covered in Figure 2, as taken from a comprehensive environmental study of a number of severe storm systems reported by Carey and Buffalo [20].…”

“…The main concern in [20] was relationship of CG polarity to cloud electrification and occurrence of lightning, specifically, to investigate the suggestion that strong wind updrafts with associated large liquid water contents in severe storms would cause an inverted lower cloud positive charge structure (changed from normally overwhelming negative charge) and lead to enhanced+CG lightning production. Such concern with CG lightning activity and strong updraft wind velocity relates to the model of tornadogenesis stemming from an important role for upward-deflected wind velocity occurring in the below cloud environment, quite different from the model description given in [12] that tornadogenesis occurs within the higher IC cloud environment consistent with the general observation that initiated tornadoes descend from above the lower cloud level.…”

Using satellite data to identify and track intense thunderstorms in South and southern Africa

“…7 Lightning data are often used for the nowcasting and tracking of convective thunderstorms 8 because of the close relationship with convective updrafts. 9,10 Aside from its relationship to convection, lightning data can also be used as a validation tool for other nowcasting tools. The objective validation for the RDT product over the European region was done by using the European Cooperation for Lightning Detection data.…”